1. Field of the Invention
This invention relates to a cooling system for a marine drive.
2. Description of the Related Art
Power driven watercraft typically include a marine drive to propel the watercraft. Marine drives typically include an engine configured to drive a propulsion device. One common type of marine drive is an outboard motor, which comprises an internal combustion engine disposed atop a drive unit. A propulsion device of the drive unit is driven by the engine. The propulsion device is positioned so that it will be at least partially submerged when the associated watercraft is disposed on a body of water. The engine includes a crankcase, a cylinder block, a cylinder head assembly, and at least several other components.
Engine operation generates significant heat. This heat can accumulate in the engine body unless properly removed. Excessive heat can jeopardize normal engine operations. Typical engines thus have a cooling system to remove heat from portions of the engine body and engine components. Various types of cooling systems are employed.
In one type of cooling system, water from the body of water in which the watercraft is being operated is drawn through a water inlet in the drive unit and is pumped through various cooling jackets in order to cool the crankcase, cylinder block, cylinder head assembly, and other engine components, as well as the exhaust system. However, in some applications, different cooling water may be used to cool portions of the engine and portions of the exhaust system. After cooling the engine and/or the exhaust system, the cooling water is returned to the body of water.
If the cooling system malfunctions such that water is no longer supplied at a desired flow rate to certain portions of the engine, the engine can overheat. This can result in serious engine failure such as seizure of the pistons and malfunction of engine components. A pilot water discharge, or xe2x80x9ctelltale,xe2x80x9d is often employed with outboard motors in order to indicate to an operator of the watercraft whether the cooling system is functioning properly. A pilot water discharge assembly generally includes a pilot water passage that branches off the cooling system and delivers a portion of the cooling water to a discharge disposed generally above the body of water. As such, the stream of discharged pilot water is easily visible or audible to the operator.
During normal operation of the cooling system, the stream of discharged pilot water will flow continuously through the pilot discharge. When the flow is continuous, steady and strong, the operator can be confident that the cooling system is working correctly. If the stream of pilot water displays abnormal behavior such as, for example, if the pilot water stream stops or is appreciably diminished, the operator will understand that there is a problem with the cooling system.
The pilot water passage generally has a small inner diameter compared to the water jackets in the engine body and exhaust system. As such, foreign objects that flow freely through the water jackets could become lodged in the relatively small pilot water passage, blocking flow therethrough. A filter is often provided at the point where the pilot water passage branches from the coolant jackets. The filter prevents foreign objects from entering and clogging the pilot water passage. Such a filter must be cleaned periodically to remove foreign debris. Cleaning of the filter takes time and effort and must be done regularly or else the efficacy of the pilot water discharge will be diminished. Also, if any components are to be cooled via the pilot water passage, cooling of such components may be diminished if the filter is not regularly cleaned.
In accordance with one aspect, the present invention provides an outboard motor comprising a power head having an engine, a driveshaft housing, a lower unit comprising a propulsion device, and an open loop cooling system. The engine drives the propulsion device and has an engine body. The cooling system has a water inlet formed through the lower unit and has at least one opening. An engine coolant passage is formed in the engine body. A pilot water passage receives a flow of water from the water inlet and directs the flow of water through at least one engine component. A minimum cross-sectional dimension of the pilot water passage along its length is never less than a maximum cross-sectional dimension of the at least one water inlet opening.
In accordance with another aspect, a marine drive is provided having an engine, a propulsion device, and an open loop cooling system. The engine is coupled to the propulsion device and has an engine body. The cooling system has a water inlet having at least one opening. An engine coolant passage is formed in the engine body and has an engine coolant discharge. The cooling system also comprises a pilot water passage. A water pump is configured to deliver water from the water inlet to the engine coolant passage and pilot water passage. The pilot water passage directs a flow of water through a pilot water discharge that is spaced from the engine coolant discharge. A cross-sectional dimension of the pilot water passage along its length is no less than a maximum cross-sectional dimension of the at least one water inlet opening.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.